Makoto Kato 6b58ba4928 Bug 1650705 - Don't dispatch unnecessary input event when we dispatch composition start with selected text. r=geckoview-reviewers,agi
Actually, before starting composition, we always remove current selected
text. So it causes that input event is fired by this operation. This is
different of Blink.

`TextEventDispatcher` can set composition string using selected text when
starting composition. So we can reduce this input event.

Also, I mistake bug 1499076 fix. By this fix, we always fires input event
when having selected text even if it is unnecessary. This changeset has
this fix too.

Differential Revision: https://phabricator.services.mozilla.com/D105464
2021-02-21 17:12:13 +00:00
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